Preparation Of Porous SrTiO₃ Nanocrystals For Efficiently Photocatalytic Activity

The fossil energy is non-renewable and not environmental friendly, which makes it necessary to explore the clean and renewable energy. Solar energy is very important clean and renewable energy except the low energy density, so that the transformation and storage of solar energy using semiconductor photocatalytic reaction are promising and potential. With the shortage of fossil fuels and serious environment problems, the photocatalytic technology such as photocatalytic water splitting and the artificial photosynthesis -namely the photo reduction of CO2, is difficult to be ignored.An ideal semiconductor photocatalyst should has a suitable energy level which matches the oxidation/reduction potential of the photocatalytic reaction, simultaneously, the crystallinity, the light absorbance and the specific surface area could also affect the photocatalytic efficiency. SrTiO3 as one photocatalyst has attracted many attentions, because it has better character in the separation and transfer of photo induced electrons and holes. Moreover, the suitable conduction band level makes SrTiO3 efficient in photocatalytic overall water splitting and also the photoreduction of CO2.To increase the photocatalytic efficiency, we try to find a way to synthesize an efficient photocatalytic SrTiO3 catalyst based on the basic semiconductor photo catalytic mechanism. Through optimizing the synthesis route, the temperature, the reaction time and the subsequent sample treatment, the sample with high specific surface area and good crystallinity was synthesized and turned out high efficient photocatalytic hydrogen productioan.Further, the method was used to synthesize transition metal doped SrTiO3 catalyst, the as-prepared sample had the CO2 photoreduction activity under visible light. The other work we done is the exploration of the influencing factors on CO2 photoreduction, which is important for the further research works. The main conclusions are as follows:Basic molten salt route was used to synthesize porous SrTiO3 nanocrystals for efficiently photocatalytic hydrogen production. Through optimizing the experimental conditions, the porous SrTiO3 nanocrystals with the largest specific surface area so far was prepared, it exhibits high rate of photocatalytic H2 evolution which is 8 times higher than that of the samples synthesized by solid-state reaction. The mixed NaOH/KOH was as the molten salts. The porous nanocrystal was formed due to the slow ions’diffusion kinetic resulting from the low reaction time, the strong basic environment and the large solution viscosity. The porous structure can be kept in the SrTiO3 nanocrystal after the removal of the basic solvent by washing in cool water, due to that the cool water can efficiently remove the dissolution heat for dissolution of strong basic matter into the water. The high photocatalytic activity of the as-prepared SrTiO3 is attributed to the high specific surface area and the good crystallinity. According to the mechanism, the molten salt method can be applied to the synthesis of ABO3 and some other complex oxides with high specific surface area.Transition metal doped nano-SrTi03 has CO2 photoreduction activity under visible light. By using molten salt method, the Fe, Co, Ni doped SrTiO3 nanoparticles were synthesized. The Co doped SrTiO3 exhibits CO2 photoreduction activity under visible light. The visible light photocatalytic activity was thought to resulted from the impurity level which induced by the doping transition metal element. Moreover, the possible influencing factors of CO2 photoreduction reaction were investigated. The results show that the most common organics such as CH3OH, C2H5OH, CH3COOH etc. would affect the reliability and the accuracy of the result of CO2 photoreduction. This is important for the further research work.